1. Field of the Invention
The present invention relates in general to temperature monitors, and in particular to a new and useful method and apparatus of accurately measuring the internal temperature of a work piece, in particular a steel work piece, in a high temperature furnace.
2. Description of the Related Art
Measuring the internal temperature of steels and other work pieces would be very useful for reduction in, among other things, process energy cost, material wastage from scale, and reduced direct production labor cost.
In a reheat furnace, for example, the primary objective is to control steel temperature, but it is not possible using current methods to measure the internal temperature of hot steel. Some steel companies use thermocouples and radiation pyrometers to measure furnace ambient temperature and steel surface temperatures. These measurements are then used along with the steel thickness/volume and time as inputs to a mathematical model to predict internal steel temperature. The difficulty with this approach is that it requires calibration which, in turn, depends on furnace and burner configuration.
Efforts have been underway in recent years to use ultrasonic methods to measure internal temperatures of hot steel. Electromagnetic Acoustic Transducers (EMATs) may be used to contact the hot steel momentarily to send and receive ultrasonic pulses through the metal. Measurement of the pulse time-of-flight is related to the internal steel temperature. See, for example, U.S. Pat. No. 4,469,425. These methods are proven, but because good contact with coupling fluid is required, the methods are limited to relatively low temperatures. These methods are not viable for in-furnace measurement of hot steel at temperatures above 2000.degree. F.
Optical techniques for measuring temperature are also disclosed in U.S. Pat. Nos. 4,448,547; 4,560,286; and 4,626,100.